The first thing to do to start off your collection is to determine what era and style of armor you are looking for. If you want it all, that makes the collection easier. If you want a specific era and specific style, pinpoint it at the beginning.
Also, at the beginning of the collection process, it is good to determine what pieces of the armor you are looking to collect. Decide if you want the full armor with helmet, chest plate, gloves, shoes, arm and leg guards or just bits and pieces to display separately.

When determining which pieces of armor you wish to purchase, keep in mind your possible display space. If you are in a studio apartment, an entire Roman Knight may not fit. A few helmets displayed on the fireplace mantel may work better. Shields and breast plates can always be hung on the wall to conserve floor display areas.

If your armor collection is going to be used as costume pieces, then you will also want to consider the sizing of the armor before purchasing it. Most places, including medievalcostumesandgifts.com, offer sizing information for their products.
If you are not looking to use your armor as costume pieces, you may also be interested in miniature versions of the armor. These will save space in your display area and often offer as many details as the full-sized replicas.

Do your research before spending your cash. Many places offer replica armor. Some of this replica armor is battle-approved. Some armor is purely only meant for costume or display purposes. Depending on what you plan on using your armor for, make sure you are aware of the differences.

Armor collections are a unique and growing interest. Armor helmets make for interesting display pieces. Researching the history behind helmet styles will make your collection even more interesting to visitors. Having a plan when starting your collection will benefit how it turns out in the end.

Most of all have fun when planning your collection! There are tons of different options for armor. Be aware of what you are looking for and enjoy the new pieces!